A typical cable television (“CATV”) network includes a head end facility from which a plurality of feeder cable lines emanate. The feeder cable lines branch off at a tap having ports. A cable drop, which may be a single coaxial cable, extends from each port to a respective user. The cable television system is a two-way communication system. A downstream bandwidth carries signals from the head end to a user and an upstream bandwidth carries upstream signals from a user to the head end.
One example of such a system is a bidirectional CATV system with a head end controlled by a system operator and with a plurality of user's televisions equipped with set top boxes or cable modems. Downstream bandwidth of the CATV system may include broadcast television channels, video on demand services, internet data, home security services, and voice over internet (VOIP) services. Upstream bandwidth may include data related to video on demand, internet access, or other services provided by the system operator. In one possible configuration, the upstream and downstream bandwidths are transmitted between the head end and the tap via optical fiber, and between the tap and the user via coaxial cable. Upstream and downstream bandwidths are typically transmitted via oscillatory electrical signals propagated along the cable lines in a discrete frequency range, or channel. Downstream bandwidth frequencies typically range from 54-1002 megahertz (MHz), and upstream bandwidth frequencies typically range from 5-42 MHz.
A personal data network may be coupled to the cable television network via coaxial cable. Often, the personal data network is a home entertainment network providing multiple streams of high definition video and entertainment. In one example, the personal data network may employ technology standards developed by the Multimedia over Coax Alliance (MoCA). The MoCA standards promote networking of personal data utilizing the existing coaxial cable that is wired throughout the user premises. MoCA technology provides the backbone for personal data networks of multiple wired and wireless products including voice, data, security, home heating/cooling, and video technologies. In such an arrangement, the cable drop from the cable system operator connects to a MoCA-certified device such as a broadband router.
The underlying technology behind the MoCA standard is utilization of orthogonal frequency-division multiplexing (OFDM) modulation, which is a modulation method wherein a large number of closely-spaced orthogonal sub-carriers are used to carry data. The signals are generated with the exact minimum frequency spacing needed to make them orthogonal so that they do not interfere with each other. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase shift keying) at a low symbol rate. In this manner, OFDM may be likened to using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. One advantage of OFDM is that problems such as attenuation of high frequencies in a long copper wire are alleviated without complex equalization filters.
A MoCA-certified device such as the broadband router interconnects other MoCA-certified components located within the premises, for example additional set top boxes, routers and gateways, bridges, optical network terminals, personal computers, and gaming systems. The personal data network allows distribution and sharing of entertainment content among the MoCA-connected devices. For example, a high definition program recorded on a set top box in the living room may be played back by a second set top box located in a bedroom. And, a high definition movie recorded on a camcorder and stored on a user's personal computer may be accessed and displayed through any of the set top boxes within the premises. The personal data network may also allow high-definition gaming between rooms.
The personal data network may utilize an open spectrum bandwidth on the coaxial cable to transmit the personal data content, such as entertainment content. For example, a cable system operator may utilize a bandwidth of frequencies up to 1002 MHz, and a satellite system operator may utilize a bandwidth of frequencies from 1550-2450 MHz. The unused range of frequencies, or open spectrum bandwidth, is 1125-1525 MHz. In another example, the open spectrum bandwidth may higher than 2450 MHz. A personal data network utilizing the open spectrum bandwidth does not interfere with any of the bandwidth being utilized by the cable television services provider or a satellite services provider.
As may be appreciated, a personal data network utilizing coaxial cable must be able to pass signals backwards through a splitter in order to properly transmit the content room-to-room. Coaxial splitters are essentially directional couplers designed to isolate splitter outputs and prevent signals from flowing room-to-room or outlet-to-outlet. The isolation is needed to reduce interference from other devices and maximize the power transfer from the point of entry to the outlets, so as to achieve the best television reception.
The MoCA standard has been specifically designed to allow signals to travel backward through splitters, termed insertion, and pass from splitter output to output, termed isolation. All coaxial outlets in a house may be reached from each other by a single isolation jump and a number of insertion jumps.
One problem with this arrangement is that, unless preventive measures are taken, the content on the personal data bandwidth may also pass through the coaxial cable drop and potentially to other users or subscribers on the cable television network.